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FSEEK(3) FreeBSD Library Functions Manual FSEEK(3)
NAME
fgetpos, fseek, fseeko, fsetpos, ftell, ftello, rewind - reposition a
stream
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
int
fseek(FILE *stream, long offset, int whence);
long
ftell(FILE *stream);
void
rewind(FILE *stream);
int
fgetpos(FILE * restrict stream, fpos_t * restrict pos);
int
fsetpos(FILE *stream, const fpos_t *pos);
#include <sys/types.h>
int
fseeko(FILE *stream, off_t offset, int whence);
off_t
ftello(FILE *stream);
DESCRIPTION
The fseek() function sets the file position indicator for the stream
pointed to by stream. The new position, measured in bytes, is obtained
by adding offset bytes to the position specified by whence. If whence is
set to SEEK_SET, SEEK_CUR, or SEEK_END, the offset is relative to the
start of the file, the current position indicator, or end-of-file,
respectively. A successful call to the fseek() function clears the end-
of-file indicator for the stream and undoes any effects of the ungetc(3)
and ungetwc(3) functions on the same stream.
The ftell() function obtains the current value of the file position
indicator for the stream pointed to by stream.
The rewind() function sets the file position indicator for the stream
pointed to by stream to the beginning of the file. It is equivalent to:
(void)fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared (see
clearerr(3)).
Since rewind() does not return a value, an application wishing to detect
errors should clear errno, then call rewind(), and if errno is non-zero,
assume an error has occurred.
ftell() and fseek(), except that the current position is stored in an
opaque object of type fpos_t pointed to by pos. These functions provide
a portable way to seek to offsets larger than those that can be
represented by a long int. They may also store additional state
information in the fpos_t object to facilitate seeking within files
containing multibyte characters with state-dependent encodings. Although
fpos_t has traditionally been an integral type, applications cannot
assume that it is; in particular, they must not perform arithmetic on
objects of this type.
If the stream is a wide character stream (see fwide(3)), the position
specified by the combination of offset and whence must contain the first
byte of a multibyte sequence.
RETURN VALUES
The rewind() function returns no value.
The fgetpos(), fseek(), fseeko(), and fsetpos() functions return the
value 0 if successful; otherwise the value -1 is returned and the global
variable errno is set to indicate the error.
Upon successful completion, ftell() and ftello() return the current
offset. Otherwise, -1 is returned and the global variable errno is set
to indicate the error.
ERRORS
[EBADF] The stream argument is not a seekable stream.
[EINVAL] The whence argument is invalid or the resulting file-
position indicator would be set to a negative value.
[EOVERFLOW] The resulting file offset would be a value which
cannot be represented correctly in an object of type
off_t for fseeko() and ftello() or long for fseek()
and ftell().
[ESPIPE] The file descriptor underlying stream is associated
with a pipe or FIFO or file-position indicator value
is unspecified (see ungetc(3)).
The functions fgetpos(), fseek(), fseeko(), fsetpos(), ftell(), ftello(),
and rewind() may also fail and set errno for any of the errors specified
for the routines fflush(3), fstat(2), lseek(2), and malloc(3).
SEE ALSO
lseek(2), clearerr(3), fwide(3), ungetc(3), ungetwc(3)
STANDARDS
The fgetpos(), fsetpos(), fseek(), ftell(), and rewind() functions
conform to ISO/IEC 9899:1990 ("ISO C90").
The fseeko() and ftello() functions conform to IEEE Std 1003.1-2001
("POSIX.1").
HISTORY
The functions fseek(), ftell(), and rewind() first appeared in Version 7
AT&T UNIX.
FreeBSD 14.0-RELEASE-p11 April 2, 2022 FreeBSD 14.0-RELEASE-p11